5.6 Best Available Technology (BAT)
149
Treatment
Method
How It Works
What It Removes
Activated carbon
filtration
As water flows through the filter contam-
inants adsorb, or stick to, the surface of
activated carbon particles.
Pesticides; organic compounds such as benzene and carbon
tetrachlo- ride; many odors; bacterial or colloidal iron or
tannins when combined with continuous chlorination; radon;
lead or copper if equipped with special media; some other
heavy metals in certain cases; chlorine; chloramines; tri-
halomethanes. Filters with molded activated carbon blocks
will treat Cryptosporidium and Giardia.
Reverse osmosis
(RO)
Contaminants are removed by forcing water
through a membrane which has microscopic
holes. Water molecules pass through the
membrane but larger particles cannot. The
membrane is flushed to remove trapped
contaminants.
Certain tastes; some pesticides; high chloride content; fluo-
ride; nitrate; lead, copper, and other heavy metals; arsenic;
Cryp tosporidium; viruses.
Ion exchange
water softening
As water passes through a resin bed in
the softener, calcium and magnesium in
the water are exchanged for sodium or
potassium which do not create the nuisance
problems associated with hard water.
As water passes through a filter made of
sand, filter paper, compressed glass wool or
other straining material suspended particles
such as sand, soil or other particles are
trapped on the filter.
Hard water (calcium and magnesium); dissolved iron; man-
ganese; will treat cadmium, copper and zinc if operated
properly.
Sediment filtra-
tion
Sediment; acidic water when preceded by soda ash feed;
dissolved iron or manganese when preceded by continuous
chlorination, ozonation or aeration; turbidity.
Distillation
Aeration
Water is heated to create steam which is
then condensed to be collected as treated
water. Contaminants removed remain in
the heating chamber or boil off into the
atmosphere.
Oxygen is introduced into the water by an
aerator. This oxidizes contaminants such as
iron and manganese, causing them to form
solids which can then be filtered out of the
water.
Sediment; high salt content; high total dissolved solids;
pesticides if properly equipped with gas vent; fluoride; nitrate;
lead, copper and other heavy metals; arsenic; bacteria.
Dissolved iron or manganese when followed by sediment
filtration; may help reduce rotten egg odor from dissolved
hydrogen sulfide gas; radon.
De-Aeration
Mix air with water to remove dissolved
gases from the water. Aeration and
Dissolved hydrogen sulfide gas; radon. De-aeration equip-
ment sometimes are very similar, but are designed for differ-
ent treatment goals.
Continuous
Chlorination
Chlorine is fed or injected into the water
to kill bacteria and other microbial con-
taminants, as well as to oxidize iron and
manganese causing them to form solids
which can then be filtered out.
Dissolved iron or manganese when followed by sediment
filtration; rotten egg odor from dissolved hydrogen sulfide gas
or sulfate-reducing bacteria (followed by activated carbon fil-
tration); bacterial or colloidal iron or tannins when combined
with activated carbon filtration; bacteria; Giardia; viruses.
Ultraviolet (UV)
radiation
As water passes through the system, a
special lamp produces ultraviolet light
that kills bacteria and other microbial
contaminants.
Ozonation
Water enters a system where ozone is
produced and mixed with the water, a
chemical form of pure oxygen,
Bacteria; Giardia; Cryptosporidium; viruses; Ozonation
destroys bacteria and other microbial pathogens and oxidizes
compounds such as iron and manganese causing them to form
solids which can then be filtered out using sediment filtration.
Cryptosporidium; Giardia; viruses.
Ultra, micro, and
nano filtration
As water passes through a filter, suspended
particles are trapped on the filter. Particles
removed depends upon the size of the pores
in the filter. Pore sizes from smallest to
largest are nanofiltration, ultra filtration and
microfiltration.
Table 5.1: Summary of Water Treatment Methods